Process for liquid/liquid extraction

ABSTRACT

A method of phase separation using ferromagnetic materials. A mixture of phases is treated with particles or granules of ferromagnetic material so that one of the phases is preferentially absorbed or collected onto or into the particles or granules. The particles or granules of the ferromagnetic material together with the absorbed or collected phase may then be recovered from the remainder of the mixture using magnetic means.

United States Patent 11 1 Weiss et al.

[ 1 Dec. 2, 1975 PROCESS FOR LIQUID/LIQUID EXTRACTION Inventors: DonaldEric Weiss, Blackburn;

Hendrik Adriaan Jacobus Battaerd, North Clayton, both of AustraliaAssignees: Commonwealth Scientific and Industrial Research Organisation;Imperial Chemical Industries of Australia and New Zealand Limited, bothof Campbell, Australia Filed: Nov. 20, 1974 Appl. No.: 525,684

Related U.S. Application Data Division of Ser. No. 138,679, April 29.1971, Pat. No 3,890,224.

Foreign Application Priority Data May 4, 1970 Australia 1083/70 U.S. Cl210/21; 210/42 Int. Cl. 1 B01D 11/04 Field of Search 210/21, 36. 39-42,210/222, 223, 296; 252/6251, 62.54,

IN MlLLlLlTRES VOLUME [56] References Cited UNITED STATES PATENTS3,259,568 7/1966 Jordan et a1. 210/21 3,349,918 10/1967 lke 210/2233,657.119 4/1972 Turbeville.. 210/36 3,796.660 3/1974 Kaiser 210/21Primary Examiner-Thomas G. Wyse Attorney, Agent, or Firm-Cushman, Darby& Cushman 1 1 ABSTRACT.

A method of phase separation using ferromagnetic materials. A mixture ofphases is treated with particles or granules of ferromagnetic materialso that one of the phases is preferentially absorbed or collected ontoor into the particles or granules The particles or granules of theferromagnetic material together with the absorbed or collected phase maythen be recovered from the remainder of the mixture using magneticmeans.

5 Claims, 1 Drawing Figure HYFLO-SUPER CEL 0-55 JTU CELlTE 530 TIME INMINUTES PROCESS FOR LIQUID/LIQUID EXTRACTION This is a division, ofapplication Ser. No. 138,679 filed Apr. 29, 1971 now US. Pat. No.3,890,224

This invention is concerned with an improved method of phase separation.

Conventional means of separating the constituent phases of a mixturesuch as, for example, allowing a mixture of liquids to separate intodiscrete layers and then removing one layer from contact with the otherlayer, or by separating a solid from a liquid by filtration, can beextremely inefficient in certain instances. For example, emulsions andcolloidal solution are particularly difficult to separate out into theirconstituent phases. Also in instances where a second phase forms a minorproportion, or even a mere trace proportion of the whole of the mixture,such as when an oil slick is present on the surface of sea water,efficient removal of such a proportion is particularly difficult. It isalso difficult to remove solids such as occur in water supplies orsewage effluents, or gelatinous precipitates, such as hydrated metalhydroxides, from aqueous media.

We have now found a method whereby different phases in a system maybeseparated, one from another, in an extremely efficient manner.

Accordingly we provide a process of phase separation, said processcomprising the treatment of a mixture of phases with ferromagneticmaterial in particulate or granular form whereby at least part of onephase of the said mixture is absorbed or collected into or onto saidparticulate or granular material and the separation by magnetic means,of said particulater or granular material, together with said absorbedor collected portion of the mixture, from the remainder of the mixture.

Although inorganic ferromagnetic materials such as, for example,gamma-iron oxide or magnetite, are of use in certain applications suchas, for example, the use of ferromagnetic materials in reducing theentrainment of water in air, in many applications it is preferred to usea synthetic polymer comprising ferromagnetic material.

One class of suitable polymers for use in a given multi-phase mixture inwhich at least one of the phases is a liquid are those which arepreferentially wetted by a liquid phase of the mixture; The wettabilityof polymers, or the critical surface tension is defined as being thelowestsurface tension a liquid in contact with the polymer can have andstill exhibit a contact angle greater than zero. Values for the criticalsurface ten sion of a number of polymers are given in Polymer Handbook(Edited by J. Brandrup and E. H. Immergut, published by J. Wiley 8:.Sons Inc., 1966) Section III, pp. 113 114. This may be used as a guideto the selection of polymers which will be preferentially wetted by aliquid but is, of course, not limiting and many other suitable polymershave been described in the art. The chemical constitution of thepolymers is not critical except insofar as the polymer should haveadequate insolubility as well as mechanical and chemical stability inthe mixture; the main criterion for selection is wettability. Thus,suitable polymers for use in our invention can be chosen from all typesof polymers such as both addition and condensation polymers; furthermoresuch polymers may be grafted onto the surface of a different polymerparticle in order to achieve the desired wetting properties. i

A second class of suitable polymers are those which will preferentiallyabsorb one of the phases of the mix- 2 ture. Suitable polymers are thosewhich will swell in good solvents for the polymer and will not do so innonsolvents. A table useful in the selection of suitable polymers ofthis class is to be found in Polymer Handbook referred to above, Section1, pages 234. Phase separation may thus be achieved if the constituentphases of the mixture comprise a good solvent and a non-solvent for aselected polymer. Furthermore, heating such polymers, when in a swollenstate, can in favourable situations cause contraction of the structureand exudation of the absorbed solvent. Certain of these polymers may becross-linked. The cross-linking of such polymers can be of two types. Inone type the cross-links are randomly distributed throughout the polymernetwork. In another type, for example with polymers of the shell type,the polymer chains are insolubilised by the ends of their chains beinggrafted on to an impervious, inert supporting core by methods known inthe art. The chain mobility in such whiskerlike structures is muchgreater than in the randomly cross-linked polymers and favours thermalcontraction of the chains provided they are in a rubber-like state.

Suitable polymers may be of natural or synthetic origin and of the typesreferred to as condensation or addition polymers, homo polymers orrandom, block or graft copolymers.

Suitable polymers are, for example, polystyrene, copolymers of styreneand polyesters, polyesters, methyl methacrylate polymers and copolymerse.g. with ethyleneglycol dimethacrylate, phenol formaldehyde resins,polyvinyl chloride, polyethylene, polyamides. These polymers andcopolymers are normally hydrophobic in character and therefore findapplication mainly in separating hydrocarbons from aqueous phases suchas for example separating oil slicks from water and also as filter aidsin non-aqueous systems.

Other polymers are, for example, polyvinyl alcohol, urea formaldehyderesins and melamine formaldehyde resins. These polymers are normallyhydrophilic and find main application as filter aids in aqueous systemsand in separating traces of a polar phase from a nonpolar phase.

The efficiency of the process also depends on the size, sizedistribution and shape of the polymer particles or granules. The greaterthe external surface area of the particles or granules the greater theamount of material which will be collected onto the surface and also themore rapidly will the process occur.

The size range of particles of use in our invention is not narrowlycritical and depends on the conditions of use. For example we have foundthat relatively coarse partilces of from 500 to 5000 microns overalldiameter are best for certain applications such as, for example removingoil slicks from the surface of the sea especially in windy weather. Foruse as filter aids smaller particles are preferred. Preferably theaverage size of the particles or granules is from 0.1 to 500 micronsoverall diameter, more preferably from 0.5 40 microns.

The amount of material absorbed or collected in or on a given weight ofpolymer particles or granules will also be increased by the presence ofvoids in the particles or granules. Such voids may be predominantlyinterconnected with the particle surface; such particles are calledreticulated or retiporous particles or granules. Alternatively the voidsmay occur predominantly as completely sealed voids; such particles aretermed vesicular particles or granules. Furthermore the'particles may beof a heterogeneous structure for example made up of layers such as ashell of one polymer grafted on and around a particle, formed from adifferent polymer with or without void. The vesicules are of particularuse in adjusting the specific gravity of particles. Particles may be ofregular shape but it is preferred that they be of irregular shape suchthat they cannot pack closely and that they have a low packing densityand increasethe volume of the void space. Such particles areparticularly useful for the separation of solid/liquid and solid/ gasphases.

The particles or granules together with the absorbed or collectedmaterial may be removed from the residual phase or phases by anysuitable physical means, such as filtration, centrifugation orsedimentation, or the like.

However, although such means are satisfactory, they are relatively timeconsuming, when the particles or granules are in the preferred sizerange. We have now found that small particles or granules of certainpolymers containing ferromagnetic materials and an absorbed phase may beremoved very efficiently from the residual phase or phases by use of amagnetic field.

Accordingly we provide a process of separating phases of a mixture onefrom the other which process comprises treating the mixture of phaseswith a particulate or granular ferromagnetic synthetic polymericmaterial so as to absorb or collect at least part of one phase of themixture into or onto said'particulate or granular material andseparating said particulate or granular material together with theabsorbed or collected portion of the mixture by magnetic means.

The ferromagnetic particles, with their absorbed material may be removedfrom the other phase (or phases) by known means described in the art,such as, for example, by direct removal with a magnetic separator or bymangetising the particles so as to induce flocculation and resultantrapid settling of the particles together with absorbed material. Thus inthe instance of a two phase system wherein one of the phases has beenabsorbed on the ferromagnetic particles and the residual phase is aliquid, the residual supernatant liquid can then be decanted from thesettled floc. The particles can remain magnetised during the process ofabsorbing the phase, the increased void volume of such magneticallyflocculated particles is advantageous as it provides additional voidspace for retention of the absorbed material.

Suitable ferromagnetic polymers have a ferromagnetic componentincorporated either wholly or partially within a layer of polymer.Subsequent layers of the same or different polymers may be grafted on oradded. The ferromagnetic component can, for example, be either a softferrite, a hard ferrite or a material which exhibits reversiblemagnetism such as gammairon oxide, magnetite or chromium dioxide. Theferromagnetic material must obviously be of a particle size smaller thanthe polymer particles to be prepared. Certain suitable ferromagneticmaterials such as for example mill scale are very expensive to grind tothe desired degree of fineness. Magnetic iron oxides, by contrast, aresimple to prepare as fine powders and are therefore convenient to usewhere a reversible ferromagnetic polymeric material is required. Thegreater ease of dispersion of an unmagnetised, reversible ferromagneticmaterial, as compared to a hard ferrite which becomes magnetic whenground to the required degree of fineness, is advantageous when thematerial is to be incorporated within polymers.

The ferromagnetic polymeric materials used in this invention may beprepared by the normal methods known in the art. Suitable methods whichmay be mentioned include the following. The magnetic material may bedispersed in a monomer or monomer mixture which may then be polymerisedto give the required particles. Another method is to compound a mixtureof a polymer and magnetic material together by a milling operation. Thefinely ground mixture may then be granulated to give material of therequired size range. In yet another method magnetic material may bedispersed in a solution of liquid polymers which may then becross-linked in a curing process. Another method is to deposit a polymeronto magnetic material by polymerisation from the vapour phase by anysuitable method known in the art. A polymer may also be precipitatedfrom a solution onto a dispersion of magnetic particles so as toencapsulate them. Methods for encapsulation are known in the art.

' The material absorbed or collected onto the particles or granules maybe recovered or removed by simple physical or chemical means. Forexample, the material may be removed by washing, pressing, distillationor by solvent extraction. In some instances, the absorbed material canbe partially removed by heating the polymer particles so as to induceshrinkage and exudation of absorbed material. The recovered particles orgranules may be reused.

There are many situations where it is required to remove very smallamounts of finely divided, or gelatinous particulate matter such asclays and organic matter from for example, surface water supplies orfrom effluents from sewage treatment plants. One such situation relatesto the desalination of water supplies by ion exchange processesutilising counter-current, reverse flow, regeneration procedures. Theefficiency of such processes relies on the development of aconcentration gradient within the bed which must not be destroyedbetween successive regeneration and absorption cycles. Consequentlyback-washing of the bed, which is required to remove accumulatedparticulate matter, must be infrequent and prefiltration of the feedwater is usually essential to reduce the rate of clogging of the ionexchange bed. When because of adverse kinetics as for example in theso-called Sirotherm process of water desalination using thermalregeneration of ion ex change resins, it is desirable also to operate anion exchange fixed bed process with resins having the smallest possibleparticle size (e.g. 50 mesh as compared with the more usual 20 50 meshstandard resins) prefiltration is an essential requirement forsuccessful operation to reduce clogging of the bed and distributors. Oneobject of this invention is therefore to provide an improvedprefiltration process for such applications. In other situations, forexample, the treatment of raw sewage itself, the separation of hydrousmetal hydroxides in hydrometallurgical operations or in chemicalprocessing, the concentration of suspended solids is much higher.

In all these instances direct filtration of the suspension is often notpractical as the result of rapid blinding of the pores of the filtermedium by the finely divided or gelatinous material. One known procedurefor increasing filtration rates in such situations is to first precoatthe filter medium with a filter aid i.e. a chemically inert solid havinga low packing density (e.g. diatomaceous earth) before starting thefiltration. In addition to forming a precoat it is also oftenadvantageous to continue to add small amounts of filter aid to the feedso as to maintain the porosity of the accumulation of filter cake (bodyfeed technique). The bed of particles provides an incompressible layerof high porosity and permits rapid filtration until the accumulation ofparticulate matter within the voids of the filter aid blocks the layer.When the concentration of suspended matter is very low (e.g. about ppm),as in some water supplies, this technique is economically feasible eventhough the filter aid must be discarded along with the filter cake.However, when the concentration of suspended solids is high, thenecessary discarding of the filter aid often makes the processuneconomic.

We have now found that our invention will allow for the easyregeneration of the phase separation aid.

Accordingly we provide a process of separating the phases in a mixturecomprising suspensions of particu late matter in a liquid medium whichprocess comprises firstly precoating a filter medium with a layer offine particles or granules of a wettable ferromagnetic material;secondly passing said mixture, optionally in admix' ture with furtherferromagnetic material, through the precoat layer on the filter mediumso as to separate the particulate matter and ferromagnetic material fromthe liquid phase; thirdly separating said ferromagnetic material fromthe particulate matter by magnetic means.

The ferromagnetic material separated and recovered by the above processmay be reused in phase separation processes, thus leading to a reductionin filter aid costs. In instances where it is desired to recover theparticulate matter, for example in chemical processing ormineral-recovery, the ease of separation of the ferromagnetic filter aidis advantageous. Preferably the ferromagnetic material is a syntheticferromagnetic polymer.

The selection of suitable polymers is not narrowly critical and can bebased on the criterion of wettability as set out herinbefore. Thepolymer should also be insoluble in the liquid medium used.

For use in polar media, for example water, typical polymers of use inour process are ferromagnetic particles incorporated wholly or partiallywithin, for example, polyvinyl alcohol, urea formaldehyde resins andmelamine formaldehyde resins.

Preferably the specific gravity of the ferromagnetic polymeric materialshould be such that the settling rate of the unmagnetised filter aid iscomparable with the settling rate of the solid phase to be removed.Adjustment of the specific gravity is achieved by methods well known inthe art, for example, for the production of vesicular particles.

We have found that shell grafted polymers are of particular use in thisaspect of our invention especially if the reactive shell contains groupssuch as polyelectrolytes which will cause flocculation of the fineparticles of suspended solid phase to be separated.

Suitable shell grafted polymers comprising polyelectrolytes are, forexample, particles comprising an inert core consisting of polyvinylalcohol or urea formaldehyde resin grafted with a shell of polyacrylicacid, polyacrylamide or polymethylacrylate or polymers derived fromquaternised amino monomers.

The separation of the solid phase from the ferromagnetic particles maybe accomplished by firstly dispersing the filter cake in a small amountof a suitable liquid by known means (e.g. mechanical or ultrasonicdispersive procedures). The ferromagnetic material is then recovered bymagnetic means for example with the aid of a magnetic separator or bymagnetic flocculation. If desired, the separated ferromagnetic materialmay be dispersed with a small amount of a suitable liquid and thenrecovered to ensure that particulate matter is not inadvertantlycontained in the ferromagnetic material prior to reuse. Repeatedmagnetisation, and demagnetisation of the ferromagnetic particles is aneffective way of dislodging attached particulate matter.

If the filter aid is magnetised, when used during the filtration cycle,the void volume, and therefore the porosity of the precoat layer, willbe greater than when the filter aid is unmagnetised. It is thereforepossible to regulate the porosity of the precoat by regulating theextent to which the ferromagnetic particles have been magnetised.

In order to obtain a uniform coating on vertical filter septums it isdesirable that the filter aid does not settle too rapidly in the feedslurry. Consequently it is advantageous to use ferromagnetic polymerparticles of the vesicular type in order to reduce their specificgravity and to apply the particles in an unmagnetised state.

In the treatment of sewage with a magnetic filter aid according to ourinvention, the filter cake with the organic particulate matter may beredispersed in a fraction of the circulating liquid stream and theresulting sludge digested. After the organic materials have beendecomposed by bacterial action the filter aid may be recovered from thehumus sludge by magnetic means and reused. Some of the supernatantliquid after the separation of humus sludge can be recirculated forredispersion of the filter aid. Similarly mixtures containiniggelatinous hydrated metal hydroxides often encountered in mineralextraction may be filtered easily, using ferromagnetic particles. Theseparticles may be reused.

The problem of removing slicks of oil from water is growing in the worldand concern over the effect of pollution on the ecology of the ocean andthe amenities of its environs is widespread. Many methods of treatingoil slicks have been proposed but these methods merely transfer theproblem to another ecological system. For example it has been proposedto emulisfy the oil with a detergent which will of course spread thepollution throughout the body of the water or for example it has beenproposed to sink the oil with heavy mineral powder such as gypsum orstucco, which will pollute the lower levels of the ocean. However, ourinvention may be used to remove oil slicks efficiently and withoutdamage to ecological systems.

Accordingly we provide a method of removing oil slicks from aqueousmedia, said method comprising: firstly, treating said slick withsufficient fine particles or granules of ferromagnetic material beingcharacterised in that said ferromagnetic material preferentially absorbsor adsorbs oil from aqueous media and also the particles or granulesfloat on the aqueous media when associated with the oil; secondlyremoving said particles together with the associated oil by magneticmeans.

Preferably the ferromagnetic material is a synthetic ferromagneticpolymer. The selection of suitable polymers is not narrowly critical andcan be based on the criterion of wettability in the oil phase. Thepolymer should also be insoluble in both the oil phase and the aqueousphase.

Suitable ferromagnetic polymeric materials for use in this aspect of ourinvention include, for example, ferromagnetic particles incorporatedwholly or partially within polystyrene or copolymers of styrene andpolyesters.

The specific gravity of the ferromagnetic polymeric particles may beadjusted by methods known in the art. Ferromagnetic vesicular andretiporous particles are convenient to use as their specific gravity isreadily controlled by methods known in the art.

A magnetic field may be, for example, generated by a boom drawn above orbelow the surface of the water. The particles and associated oil may beremoved from the boom by any suitable mechanical means eithercontinuously or periodically.

A further advantage of using ferromagnetic particles or granules forphase separation is that the force of the magnetic field used forcollecting the said particles or granules is such that it will exertsufficient pressure on the particles or granules for them to assume acompact form without however, squeezing the collected phase from betweenthe particles. A still further advantage of using certain ferromagneticparticles or granules is that after collection the particles or granuleswill be magnetised and will tend to clump together and adhere to anyferromagnetic material. Therefore they may be easily conveyed by meansof ferromagnetic belts or other conveyor means. The particles orgranules may be easily demagnetised by passing them through any suitabledemagnetiser. it is sometimes advantageous to use a soft ferritecontaining polymer as such a polymer may be dispersed more readily so asto facilitate its application to an oil slick, for example, by aspraying technique. Such soft ferrite materials are strongly attractedby a magnetic field and can therefore be collected readily by magneticmeans.

Our invention is also of use in a phase separation problem encounteredin cooling towers. In normal operation of cooling towers water flowsover a packing, or is sprayed countercurrent to an air fiow and there isoften a substantial loss of water due to the entrainment of waterdroplets by the exit air stream. This is of course an example of aliquid/gas phase system and suitable hydrophilic ferromagnetic particlesmay be dispersed in the water entering the tower, to allow the air andwater to be separated more efficiently, by increasing the settling rateof the water droplets and to permit their trapping by magnetic means.

Magnetised particles are usually preferred, for use in such a processbecause the void volume, and settling rate of magnetised particles isgreater than that of unmagnetised particles. Magnetised ferromagneticparticles, encapsulated with a polymer are more readily redispersed andare therefore particularly useful.

Accordingly we provide a process of separating liquid and gas phaseswhich process comprises the separation of droplets of a liquidcontaining ferromagnetic materials wettable by said liquid, entrained ina gas stream by magnetic means.

In applying the method to a cooling tower the feed water to the tower isfirst mixed with ferromagnetic particles and the slurry then passedthrough the tower, countercurrent to an air stream. At the base of thetower there is a settling basin where the particles are removed from thecooled water by magnetic means. Spray loss from the tower is reducedbecause the droplets settle more rapidly owing to their containingferromagnetic materials; however any droplets entrained in the exit aircould be recovered by magnetic means. For example, droplets containingsuch magnetic particles in the exit air may be passed over baffles ofpolymers loaded with magnetised particles e.g. barium ferrite andpreferably with water repellant surfaces e.g. a fluorinated hydrocarbon.This attracts the magnetic water particles and thereby reduces losses.The particles accumulate on the surface through the coalescing effect ofthe water film, growing in size until they eventually slide off themagnetic surface. Other magnetic devices may be utilised to facilitateremoval of the water from the magnetic particles.

The particles may be inorganic ferromagnetic materials or ferromagneticmaterials encapsulated by hydrophilic polymers, or encapsulated byhydrophobic polymers with surfaces of a hydrophilic nature graftedthereon.

To these polymeric magnetic particles may be attached algicides or thelike to inhibit slime growth in the tower. The magnetic particles maybe, for example, soft ferrites, hard ferrites or intermediate materialssuch as gamma-iron oxide.

Another phase separation problem which benefits from the use offerromagnetic polymeric particles is the sealing of pipe joints,particularly where a united mobility in such joints is desired, such as,for example, in the sealing of joints in sewerage pipes or gas pipelines. Owing to soil movement it is extremely difficult to preventcracks developing at the joints of underground pipes. Liquids from theground, for example, water, percolate through such joints and this ismost undesirable as in sewage pipes for example it increases the volumeof effluent for disposal or treatment and raises the salinity of theeffluent when the ground water is saline.

We have now discovered that when the surfaces of the joints in pipes aremagnetised and the space between the magnetised surfaces is packed withfinely divided, hydrophobic magnetised particles having surfaces whichare not wetted by water, the magnetic field holds the particles inplace, even when the joints move, and the water repellency of theirvoids prevents entry of water. A refinement is to form a paste havingthe consistency of a grease with the hydrophobic ferromagnetic particlesand an oil which preferentially wets the particles and which is highlyresistant to microbiological attack e.g. fiuorinated hydrocarbons orsilicones. The paste is then applied to the magnetic joints.

The magnetic surfaces in the joints may be for example a layer ofmagnetic material either bonded with a cement e.g. portland cement orbonding adhesives stable in the environment.

Accordingly we provide a method of sealing pipes, with a flexible joint,such that fluid may not percolate into or out of the pipe through thesaid joint, said method comprising the use of a sealant comprising acomposition of a finely divided ferromagnetic particles optionally inthe presence of a stable oil, said oil wetting the said particles, andthe use of said sealant in the joints of magnetised pipes whereby themagnetic force of the pipes holds the sealant in place in the joint.

Our process may also be used in the separation of solid and gas phaseswherein the solid phase is separated from a gas phase, for example, theremoval of solid particulate matter from flue gases, by passing themixed phases through a filtration device comprising ferromagneticmaterials.

The process of our invention is also of use in liquid/- liquidextraction. When a liquid medium contains a very small concentration ofa given material it is often difficult or expensive to extractefficiently the material into a second liquid medium. For exampleaqueous so- 9 lutions containing metal salts may be treated withcomplexing agents to form complexes such as chelates soluble innon-polar solvents. However in the past relatively large amounts ofnon-polar solvent have been required to remove small amounts of.complexes because of the difficulty of separating the aqueous andorganic phases efficiently and the process has therefore been expensivefor removing trace impurities. We have found that our process of phaseseparation may be employed to separate the phases after a liquid/liquidextraction and particularly when one phase is a small proportion of thewhole composition. This embodiment of our invention has the advantagethat by its use trace impurities may be removed from effluent fromchemical, municipal and industrial plant process streams andmetallurgical operations in an economical manner.

Accordingly in the process of liquid/liquid extraction comprisingextracting a compound from a solution of the compound in a liquidmedium-with a second liquid medium immiscible with the first liquidmedium we provide the improvement consistingof separating the two liquidphases by firstly adding ferromagneticparticles being characterised inthat said ferromagnetic particles preferentially absorb or absorb thesecond liquid medium; and seondly removing'said particles together withthe associated second liquid medium by magnetic means. This embodimentof our invention although of use for separating any proportions of thetwo liquid media is of especial use when the second liquid media is onlya minor proportion of the total composition, for example less than 10%w/w of total composition.

In order to work a liquid/liquid extraction process efficiently usingsmall proportions of. extracting liquid it is desirable for the twoliquids tobe mixed together extremely well. This thorough mixing canlead to emulsions which render the prior art methods of separation ofphases extremely inefficient. The process of our invention howeverseparates the constituent phases of emulsions without difficulty.

In order to remove certain compounds from solution it is desirable toadd suitable complexing agents either directly to the first liquidmedium or dissolved in the second liquid medium. The purpose of thesecomplexing agents is to form a complex with the compound which complexhas a more favourable partition coefficientthan the compound forextraction by the second liquid medium.

The nature of the complexing agent depends upon the nature of thecompound to be removed. The complexing agent should form a complex withthe compound to be removed. The nature of the second liquid mediumdepends upon the nature of the first liquid medium and also upon theproperties of the complex found between the complexing agent and thecompound to be removed. In liquid/liquid extractions it is desirableforthe two media to be mutually insoluble and for the complex to befreely soluble in the second liquid medium and sparingly soluble in thefirst liquid medium. Suitable combinations 'of liquid media andcomplexing agents for liquid/liquid extractions are well known in theart. It is possible to choose an organic liquid medium which acts bothasthe second liquid medium and as the complexing agent and use of suchan organic liquid medium falls within thescope of our invention.

Although the ferromagnetic particles may be any particles with therequired characteristics we prefer 10 that the ferromagnetic material isa synthetic ferromagnetic polymer.

In liquid/liquid extractions of trace materials from an aqueous solutionwith a non-polar media suitable synthetic ferromagnetic polymers are asdescribed hereinabove as suitable for the removal of oil slicks fromwater. This embodiment of our invention is of particular use in removingsmall amounts of metals salts from the process streams and effluents ofhydrometallurgical mining operations.

Our invention is illustrated in, but not limited by, the followingexamples, in which all parts and percentages are by weight unlessotherwise stated, and the accompanying drawing (FIG. 1), which comparesflow rates using the resins of the invention on the one hand and knowncommercial resins on the other.

EXAMPLE 1 This is an example of the preparation of a ferromagneticpolymeric particle of use in our invention.

A dispersion of gamma-iron oxide was prepared as follows:

Bayer Sll gamma-iron oxide (Trade Mark for a gamma-iron oxide) (51 g.)was added to a solution of 5.1 g. of Teric PE68" (Trade Mark of ImperialChemical Industries of Australia and New Zealand Limited for an alkyleneoxide condensate) in 400 mls of water and stirred vigorously until thedispersion consisted of clusters of oxide particles smaller than 5microns.

A solution of polyvinyl alcohol (491 mls of a 20% solution w/v) and 2 g.of Gelvatol 20-30 (Trade Mark for a polyvinyl alcohol) was added and thesuspension stirred until it consisted of clusters of oxide particlessmaller than 5 microns.

To the above suspension was added a 25% aqueous solution ofglutaraldehyde (200 mls) and 2 N.I-ICl (70 ml) with rapid stirring. Thesolution was immediately dispersed into 2 I. of kerosene to which hadbeen added 40 g. of Span (Trade Mark for sorbitan mono-oleate) and 10 g.of Tween (Trade Mark for a polyoxyethylene sorbitan mono-oleate).

Vigorous stirring was continued for one hour followed by gentleagitation for about 6 hours. The product was filtered off, washed withkerosene, hexane and finally acetone until the filtrate was clear. Theparticles so obtained were dried and cured for 1 hour at C. g. ofparticles were obtained with an average size of 10 microns andcontaining 60% w/v of gamma-iron oxide.

EXAMPLE 2 This Example demonstrates the ease with which a dispersion offerromagnetic particles may be settled out from a liquid. The particlesobtained in Example 1 (l g.) were dispersed by shaking with 100 ml. ofwater in a 200 ml stoppered measuring flask. The dispersion took morethan 20 minutes to settle. However, when a similarly prepared dispersionwas held over a strong magnet the dispersion settled in a few seconds.The settled particles were demagnetised in an apparatus described by G.W. Davis (Physics 6 184 (1935)).

The demagnetised particles could be redispersed to yield a dispersionhaving the same properties as the initially prepared dispersions. Whenthe magnetised particles were redispersed without demagnetisation, theso formed dispersion settled in a few seconds.

The particles were magnetised and demagnetised many times without damageto the particles.

EXAMPLE 3 This is an example of the preparation of a shell graftedparticle suitable for use in our invention.

The particles (26.7 g.) prepared in Example 1 were added to 100 mls ofstyrene. The mixture was purged with nitrogen and irradiated in anitrogen atmosphere with Cobalt 60 gamma-rays at a dose rate of 0.11 M.Rad/hr. to a total dose of 5.1 M. Rad. The particles were removed andwashed with benzene until free of homopolymer and finally washed withmethanol and dried under reduced pressure at 65C. 56.4 g. of particleswere obtained containing 52.7% of polystyrene.

EXAMPLE 4 This example demonstrates the removal of an oil slick from thesurface of water.

To a 12 inch dish containing 100 ml of water was added 1 ml of crudeoil. The particles (approximately 200 mg.) prepared in Example 3 weredusted over the surface. The particles were wetted by the oil and when amagnet was moved close to the surface of the water the particles andassociated oil were removed leaving an almost clean surface.

EXAMPLE 5 This is an example of destroying an oil slick by bummg.

Water (100 ml) and crude oil (1 ml) were placed in a 12 inch dish. Theparticles prepared in Example 3 were magnetised by placing them in astrong magnetic field for a brief time. The magnetised particles soprepared (100 mg) were placed in the centre of the oil slick preparedabove. The oil was attracted towards the small clump of particles. Theparticles formed a wick and the oil was ignited and removed by burning.

EXAMPLE 6 Examples 6 to 9 describe the preparation of vesicularpolystyrene particles of use in our invention.

A mixture of fumaric acid, phthalic anhydride and propylene glycol inthe molar proportions of 3:114 respectively, with an acid value of 38and Gardner Holt body Z2 at 70% w/w in styrene was prepared. To thispolyester solution (29.5 lbs.) was added with high speed stirring, 11.8lbs. of styrene, 1 lb. of benzyl peroxide (55% w/w in dibutyl phthalate)and lbs. of S1 1 gamma-iron oxide. The mixture was stirred until all thecompounds were well dispersed.

A second mixture was prepared by mixing water (66 lbs), a 2.25% w/whydroxyethyl cellulose concentrate (8.25 lbs.), Gelvatol 20/90 (5.5lbs.) (Trade Mark for a polyvinyl alcohol), diethylene triamine (51 g.)and aqueous ammonia s.g. 0.88 (3.74 g.).

The first mixture was added under vigorous stirring by means of a flutedstirrer to the second mixture. More water (110 lbs.) was added and afterflushing with nitrogen the mixture was heated at 90C for 2 hours whenthe polymerisation was virtually complete. After polymerisation themixture was diluted 5-fold with water and the particles allowed tosettle, washed by decantation and dried at 105C. Vesicular particleswere obtained containing an average of 50% void space. The averageparticle size was l5-20 microns.

EXAMPLE 7 Example 6 was repeated except that the gamma-iron oxide ofthat Example was replaced by Ferrox cube 12 3E (Trade Mark for a softferrite). This is an example of the preparation of a vesicular particlewith soft ferrite properties.

EXAMPLE 8 Example 6 was repeated except that the gamma-iron oxide ofthat Example was replaced by Black iron oxide 318M (Trade Mark for ahard ferrite). This is an Example of the preparation of a vesicularparticle with hard ferrite properties.

EXAMPLE 9 Example 6 was repeated except that only 3 lbs. of styrene wasused instead of the 11.8 lbs. used in that Example. The particles formedin this example were of irregular shape.

EXAMPLE 10 This is an example of the removal of oil slicks on watersurfaces and the recovery of the polymer for reuse. Fuel oil (10 mls)was placed in a 12 inch dish containing 100 ml of water. Polymerparticles (5 g.) prepared in Example 6 were dusted over the oil slickand the contents of the dish were vigorously stirred. The particlesfloated to the top of the water associated with most of the oil, and theoil and particles were removed using a magnet covered with a thinpolythene film. The particles were separated from the associated oil byvacuum filtration when 7 mls of oil were recovered. The recoveredparticles were reused repetitively to remove fresh oil slicks preparedas above.

EXAMPLE 1 1 Example 10 was repeated using the particles prepared inExample 7 in place of the particles prepared in Example 6. Similarresults were obtained as in Example 10 except that as the particles wereprepared from a soft ferrite it was easier to remove the particles fromthe magnetic field and also redispersion on recycling the particles waseasier as little permanent magnetism was induced in the particles.

EXAMPLE 12 To an oil slick prepared as in Example 10 there were addedthe particles (5 g.) prepared in Example 8. The particles were drawntogether by a magnet to the centre of the dish forming a clump ofparticles, held together by magnetic forces. The particles and oil wereset on fire and burned until nearly all the oil was removed from thesurface, leaving a non-polymeric iron oxide sludge which settled to thebottom of the dish.

EXAMPLE 13 This illustrates the use of a polymer particle for theremoval of very fine droplets of water dispersed in an oil. Theparticles were prepared as follows.

A mixture of a 25% aqueous solution (4.55 ml) of glutaraldehyde and 2 g.of gamma-iron oxide was added to 50 ml of a 20% w/v aqueous solution ofGelvatol 20-30, and after being thoroughly mixed the whole was acidifiedby addition of hydrochloric acid (2 N; 2.87 ml). The mixture was stirredby hand for 15 see. before being dispersed into droplets by addition tostirred mineral oil (200 ml; Ondina 33 Trade Mark of Shell Oil Co. Ltd.)at ambient temperature. After continuous mechanical stirring for 45minutes, the temperature of the suspension was raised during 15 minutesto C and maintained at that level for a further 20 minutes. Thecross-linked polyvinyl alcohol particles thus formed were separated fromthe cooled mixture, washed with hexane to remove adherent oil, then withacetone and finally with water, in a column, until the effluent was freefrom chloride ion and had a pH of or greater. The washed product waspartially dehydrated by treatment with acetone and finally dried invacuo at 5()60C. for 24 hrs, to yield hard particles of cross-linkedpolyvinyl alcohol in the size range 0.5 5 microns. The size of theparticles within this range was controlled by varying the stirring speedduring their preparation.

When a suspension of fine droplets of water in kerosene was added to thedried beads at room temperature they rapidly absorbed the water. Whenthe beads had absorbed about 50% by weight of water they were fullyswollen. On heating them to 80C they shrunkand 35% by volume of wateroozed out of the beads and was removed. After the beads were cooled theycould reabsorb water.

When water continued to be added to the fully swollen cold particlesthey joined together as a film of water developed around the particlesand encased them. The swollen particles and associated water wereremoved from the kerosene by means of a magnet covered with polythenefilm. The particles and associated water were removed from the magnet bypulling off the polythene film.

In a comparative experiment particles were prepared by a similar methodbut without using any ferromagnetic material. It was found that althoughthese particles absorbed the water satisfactorily they could not beseparated from the kerosene easily unless the minimum size of theparticles was about 100 microns.

EXAMPLE 14 This Example demonstrates the use of the invention inremoving a fine suspension of clay from water.

3 g. of the beads prepared in Example 9 were suspended in water andpoured into a 1 inch glass funnel (porosity 2) on which was placed aclose fitting Whatman No. 54 (Trade Mark) filter paper to form a filterbed. The beads were unmagnetised.

A bed was formed approximately one-fourth inch deep. Water filteredthrough this bed at a rate of 10 ml per minute under a constant head of7 inches.

A suspension of kaolin in water was prepared by decantation from acoarse suspension. This suspension had a turbidity of 40 Jacksonturbidity units (JTU) which was unchanged when passed through a WhatmanNo. 54 filter paper. This suspension was filtered through the bed of thefilter aid. The filtrate was clear.

TABLE I Amount of Suspension Turbidity reading filtered of Filtrate JTUAfter 50 ml 2.3 After 100 ml 2.4 After 150 ml 2.7 After 200 ml 1.5

TABLE 11 Suspension passed Turbidity Readings After 50 ml 5.0 .ITU Afterml 4.5 .lTU After 200 ml 1.5 JTU The filtration rate at a head of 7inches fell steadily from 9 ml/min. to 2 ml/min. after passage of 300ml. The results are given in Table 11.

However, the filter aid could not be cleaned by elutriation because thesettling rate of the Hyflo Supercel was too low.

EXAMPLE 15 This Example compares the effect of using the particlesprepared in Examples 6 and 9, in a magnetised an unmagnetised state asfilter aids; with the effect of using Hyflo Supercel and Celite 545(Trade Mark for a diatomaceous earth).

The particles prepared in Examples 6 and 9 were magnetised by passingthem briefly through the poles of a large shoe magnet.

Turbid water was prepared by decanting the fine material from asuspension of kaolin and diluting this with tap water to a standardturbidity of 40 Jackson Turbidity Units (JTU). The filter bed was ineach case prepared by the following method. A disc of Whatman No. 54filter paper was inserted into a 3 cm. diameter sinter glass tubefilter, porosity 2. The filter aid was dispersed in water, and thedispersion poured onto the filter paper.

Six beds, A, B, C, D, E and F, were prepared of the following materialsrespectively:

Bed A: 2 g Hyflo Supercel Bed B: 2 g Celite 545 Bedl Cg 3 g unmagnetisedmaterial prepared in Examp e Be6d D: 3 g magnetised material prepared inExam le Bed E: 3 g unmagnetised material prepared in Example 9 Begd F: 3g magnetised material prepared in Example The magnetised materialsformed a deeper bed than the unmagnetised materials.

Samples of the turbid water were filtered through each of the six beds,A, B, C, D, E and F, prepared by the above method, and an average headof 15 cm. was maintained. The filter beds C, D, E and F were back washedusing clean water. After agitation the filter aids where allowed tosettle and the turbid wash water decanted off. After three back washingoperations the filter beds were reused and had unimpaired efficiency. Itwas noted that the magnetised materials had the higher settling rates.The beds, A and B, formed from Celite and Hyflo Supercel could not bebackwashed in this manner. The rates of filtration and the efficiency offiltration for each of the six beds are given in Table III.

The results demonstrate that the ferromagnetic particles of ourinvention are superior to Celite 545 whether they be magnetised orunmagnetised and in comparison to Hyflo Supercel they have enhancedfiltration rates and the unmagnetised particles are similar in theirefficiency of removal of turbidity. The ferromagnetic particles of ourinvention have the added advantage that they may be recovered and reusedin phase separation processes whereas the diatomaceous earths cannot beso recovered.

TABLE III BED A BED B Volume Time Turbidity Time Turbidity ml min. JTUmin JTU 5O 6 6.5 1.2 12 100 16 1.7 3.0 14 150 24 9 4.5 12 200 33 0.5 6.2l l 250 49 0.5 8.0 12 300 65 0 3 10.0 12 350 85 3 12.2 12

BED C BED D Volume Time Turbidity Time Turbidity ml min. JTU min JTU BEDE BED F Volume Time Turbidity Time Turbidity ml min. JTU min. JTU

EXAMPLE 16 This Example demonstrates the use of our invention inseparating viscous suspensions formed in chemical processes. A slurrywas obtained from a polymerisation reaction. This slurry contained a 5%w/w suspension of 4-6 micron cross-linked polyacrylic acid beads in anaqueous reaction medium comprising linear polymer and other by-productsand was highly viscous. When filtration was attempted, with variousgrades of previously known filter aids, no more than a few drops couldbe filtered before the filter became blocked each time by a layer of gelon the surface of the septum. A precoat layer of the particles preparedin Example 6, was formed on a monofilament polypropylene filter cloth'(2/2 Twill, 68 X 30, 8.5 02. /sq. yd.) as a bed 0.2 cm.

deep, on a filter 23 cm in area. 5.0 g of the particles prepared inExample 6 were suspended in 25 ml of the resin suspension as body feed.Filtration of the suspension through the precoated septum then proceededat the rate of 1 ml/min. until the filter cake was dry. The upper layerof filter cake was resuspended in water and the particles removed fromthe resin by magnetic means. By such means it was possible to separatethe 16 polyacrylic acid beads from the dissolved by-products present inthe slurry after completion of the polymerisation reaction.

EXAMPLE 17 This example describes the preparation of magnetic particlesof irregular shape and size and comprising an urea formaldehyde resin.

326 g of black iron oxide 318M were dispersed by suitable means in 326 gof urea formaldehyde syrup (Mouldrite" A256, Registered Trade Mark ofImperial Chemical Industries of Australia and New Zealand Limited) towhich was added 15 g TericPE68 (Trade Mark of Imperial ChemicalIndustries of Australia and New Zealand Limited for an alkylene oxidecondensate) until the oxide was unagglomerated.

This dispersion was added to 1300 ml ortho-dichlorobenzene with 13 g ofSpan (Trade Mark Imperial Atlas for a polyoxyethylene sorbitanmonooleate) with stirring. Stirrring was continued Stirring a constantrate for 15 30 minutes. 15 ml of 2N. hydrochloric acid were added andthe resin was allowed to gel; 300 ml of ortho-dichlorobenzene were addedand stirring continued for 1 hour. Curing was completed under gentleagitation for 12 hours at room temperature. The beads were thenfiltered, ortho-dichlorobenzene was removed by steam distillation andthe beads were dried in an oven at C.

The magnetic particles so obtained were designated FA the experiment wasrepeated with a different stirring rate to give a preparation ofmagnetic particles designated FA EXAMPLE 18 The two samples of magneticparticles FA and FA prepared according to the method of Example 17 weretested using the method described in Example 14. 1.5 g of magneticparticles were suspended in water and poured into a 1 inch glass funnelwith a sintered glass disc (porosity 2) on which was placed a closefitting Whatman No. 54 filter paper to form a filter bed. The bed formedwas approximately one-fourth inch deep.

A suspension of kaolin in water was prepared by decantation from acoarse suspension. This suspension had a turbidity of 12.5 Jacksonturbidity units (JTU) which was unchanged when passed through a WhatmanNo. 54 filter paper. This suspension was filtered through the bed offilter aid under a head of 37.5 cm.

Two filter aids designated FA and FA were tested in the unmagnetised andmagnetised form, (indicated by the prefix D and M respectively) andcompared with Hyflo Supercel and Celite 503 as filter aids.

FA had an average particle size of 50 75 microns and FA had an averagesize of 25 microns. Celite 503 had an average particle size of 15microns and Hyflo Supercel had an average size of 11 microns.

In FIG. 1 the volume of clay suspension passed through the bed isplotted against time and the average turbidity of the product waterindicated against the curves so obtained. It can be seen from thesecurves that considerably better flow rates were achieved than with thecomparative commercial samples and that the blinding of the bed occurredmuch later.

The magnetised particles form beds with better flow rates than theunmagnetised ones, without substantially reducing the quality of theproduct water.

, EXAMPLE 1Q M p This example demonstratesthe reuse offilter, aids. Thefilter aids FA andFA used in Example 18 were removed from the testapparatus, placed in-aglass tube, suspended in 10 mls of waterbyvigorous shaking and settled by attraction in a magnetic field. Thesupernatent liquid was decanted retaining the filter aid with a magnetheld near the side of the-tube. The clean filter EXAMPLE 22 Filter aidFA, from Example 18 was used both in the magnetised state (M-FA and inthe unmagnetised state (D-FA,) to filter a number of different watersand effluents and its efficiency was compared with similar use of Celite503.

The results are given in Table IV below expressed as the turbidity ofthe product water after 100 ml had aid was then again tested asinExample'18, after passpassed through the bed under the test conditions set ingthrough a demagnetisation cycle.

out in Example 18.

i TABLE IV Flow rate 7 Feed Product after 100 Filter Turbidity Turbiditymls in Aid Type of Feed .lTU .ITU mls/min M-FA, Tap water 4.5 0.3 50Celite 4.5 0.6 10

503 D-FA, Effluent from 19.6 0.1 40

5 an autoclave being used for polyvinyl chloride y manufacture Celite19.6 0.7 7 503 j: M'-FA, River water 8.5 0.5 50 ,1 Celite 8.5 0.7 9

EXAMPLE 23 The filter aids performed as before giving the samefiltration characteristics as previously shown in FIG. 1 for theunrecycled filter aids.

EX MPLE.

This example describes a shell:- grafted filter aid.

A resin prepared-by the general method described in Example 17, with aparticle sizof 250 micron, was treated as follows. 1

20 g of resin, 20 ml of 2-vinyl pyridine and 20 ml of methanol wereplaced in a 100ml round bottom flask fitted with nitrogen inlet andoutlet tubes, the end of the inlet tube dropping into the'liquid. Thesample was purged with nitrogen for '5 minutes and then irradiated withgamma rays from 21 Cobalt 60 source at room temperature at-a dose rateof 0.3 megarad per hour to-a total dose of 6 megarad. The .sample afterirradiation was washed with methanol till freeof homopolymer. Theresultant resin was then treated with a solution of 20 ml of cetylbromide'in 80 ml 'of ethanol under reflux for 24 hours. :11

The resin was then filtered, washed with ethanol'until free of cetylbromide and dried in vacuo at 60C overnight. K r

A resin was obtained whichhad 1% by weightpolyvinyl pyridinium cetylbromide grafted to the surface;

EXAMPLE 21 I M The ungrafted resin and the shell grafted: resin'bothprepared as in Example 20 weretested by the method described in Example18 in the magnetised form. The

ungrafted resin had no effect andv the turbidity of the 1 The generalprocedure of Example 1 was repeated to give a resin having an averageparticle size of 50-100 microns. 120 g of the product was slurried with240 ml of water in a jacketed reactor. Oxygen was passed through thestirred slurry while the slurry was irradiated at 5C for 20.5 hours at adose rate of 0.344 megarad/hr (total dose 7.1 megarad). During the lastfive minutes of irradiation the oxygen was replaced with nitrogen. Asolution of 5.5 g ferrous ammonium sulphate (-Fe(NH (SO .6I-I O) in 30ml of water was added immediately and the mixture allowed to stand for 5minutes. g of acrylic acid were added quickly during which addition thetemperature rose from 5C to 8C. The mixture was cooled to 5C and stirredfor 1 hour,

filtered, washed with water anddried in vacuo at 60C.

145.8 g of grafted resin were obtained which corresponded to 17.7%grafted polyacrylic acid.

The magnetised grafted resin was compared with the This exampledescribes the preparation of vesiculated magnetic polystyrene particleshaving difierent particle sizes and porosities and suitable for theremoval of oil slicks from water.

The general procedure of Example 6 was repeated using the following foursets of ingredients shown in 19 Table VI to give four samples of resinsA, B, C and D respectively. The polyester solution was as used inExample 6.

TABLE VI Resin Ingredients A B C D Polyester Solution 72.5 g 72.5 g 72.5g 72.5 g Styrene 55 5 g 55.5 g 55.5 g 55.5 g Triten X45 l 0 g Teric X51.0 g l 0 g Topanol A 0.13 g Water 228g 61 g 91.0g 91.0gDiethylenetriamine 0.57 g 0 57 g 0.57 g 0.57 g Black Iron l5 Oxide 318M61 g 61 g 61 g 61 g NH 0.5 g 0.8 g 0.8 g 0.8 g Cumene Hydroperoxide 3.0g 3.0 g 3.0 g 3.0 g Water 750 g 1000 g 1000 I000 1200 g 1200 gHydroxyethyl cellulose 1.0 g 1.0 g 1.0 g Methyl cellulose l 0 g Gelvatol7 /27: 20/90 30.0 g 30 g 30 g 30 g The resins obtained had the physicalcharacteristics shown in Table VII.

TABLE VII Average Density Porosity Resin Size g/ml 7:

A 3040 my. 0.45 74 B 100 m 1.09 38 C 10-30 mp. 0.78 55 D 800 0.58 69 3 5EXAMPLE 25 The resins A, B, C and D prepared in Example 24 were testedto determine the effect of porosity and particle size on oil pick-upefficiency. 20 g of Kuwait crude oil was added to four Petri dishescontaining water. After 5 minutes exactly 1 g of each of the resins A,B, C and D separately was applied to the oil. A large horse-shoe magnetplaced inside a plastic bag was used to attract the resin and associatedoil. To make sure all the resin was removed from the oil surface anotherapplication of the magnet in a clean plastic bag was used. The weight ofthe oil picked up was determined. This was expressed as Weight of oilpicked up 100 Similar experiments were carried out for crude oils ofdiffering origins and using both sea and river water.

The results obtained in these experiments were similar and averagedaround 450.

EXAMPLE 26 This example describes the use of magnetic resin particles toreduce water spray.

A 6 inch diameter tube 6 feet in length, closed at the bottom and top,was provided with a nozzle at the bottom and a 1 inch side arm near thetop. The nozzle was connected to a compressed air supply via aregulating valve.

In the tube was placed 1 litre of tap water and the air turned on to 30psi causing a spray of air and water to rise in the tube. After 30minutes 250 ml of water was lost through the side arm in the form ofspray and mist.

The experiment was repeated but to the water was added 100 g of a resinprepared as in Example 1 with a particle size of 5 microns.

A 4000 gauss horse-shoe magnet was placed with the pole piecesstraddling the side arm. After 30 minutes under the same conditions asused before only mls of water was lost.

EXAMPLE 27 The preparation described in Example 17 was repeated to givea resin having a particle size of from 50 to microns. A filter bed wasprepared by precoating a coarse polypropylene screen with the resin to adepth of 0.5 inches. The filter bed was treated with 0.02% by weight ofPrimafioc C5 (Trade Mark for a water soluble cationic polyelectrolyte ofthe polyamine type). Water obtained from the Yarra River having aturbidity of 10 JTU was filtered through the bed under a gravity head of1.2 feet. The flow rate was initially 0.6 gal/min/ft and had fallen to0.34 gal/min/ft after passage of 200 bed volumes. The filtrate initiallyhad a turbidity of 0.1 .ITU and after 200 had a turbidity of 0.48 JTU.

The precoat was backwashed, using a magnet to retain the resin andfiltration recommended. The flow rate under the same conditionscommenced at 0.7 gal/- min/ft and gradually fell to 0.27 gal/rnin/ftafter 400 bed volumes had been filtered.

The turbidity of the product varied between 0.7 and 1.5 JTU.

The precoat was backwashed again, and on replacement gave substantiallythe same results.

This cycle as repeated many times.

EXAMPLE 28 A sample of the shell grafted resin prepared in Example 20was used as a filter aid to filter sewage. A filter bed was prepared byprecoating a coarse polypropylene screen with the shell grafted resin toa depth of 0.5 inches. Raw sewage obtained from a sewage plant having aturbidity of 52 .lTU was filtered through the bed under a level of 1.2feet. The initial flow rate was 1.2 gals/min/ft and after 20 bed volumesthe flow rate had fallen to 0.12 gals/min/ft the filtrate obtained hadan average turbidity of 0.5 JTU and had only 50% of the initial C.O.D.

The bed was backwashed, replaced and reused to give substantially thesame result.

The experiment was repeated using as feedstock the overflow from theprimary sedimentation stage at a sewage plant. The feed had a turbidityof 35 JTU. The initial flow rate was 0.42 gals/min/ft and after 20 bedvolumes this had fallen to 0.1 ga1s/min/ft The average turbidity of theproduct water was 0.03 JTU. After backwashing and repeated magnetisationand demagnetisation of the resin the precoat was replaced and theexperiment repeated. Substantially the same results were obtained. Thiscycle of operation was repeated many times.

EXAMPLE 29 A liquor derived from biological leaching of copper orecontained 1.0 grams per litre of Cu at a pH of 3.5. It was extractedwith 0.3 volumes of a 25% solution of 2-hydroxybenzophenoxime inkerosene, which was embodied in a floc of the synthetic ferromagneticpolymer prepared in Example 24 and designated resin A. The liquor wasextracted in a countercurrent system comprising three stages of mixing,separated by three stages of settling, in which the flocs weretransferred by magnetic means countercurrently to the flow of leachliquor.

The organic extractant attained a concentration of 3.0 grams per litreCu, and was stripped by sulphuric acid in a countercurrent system offour stages, to yield a recycle stream of organic extractant, and asolution of copper sulphate, from which the copper was recovered byelectrolysis.

EXAMPLE 30 An effluent from a petrochemical plant contained ppm ofdissolved copper and was extracted with 0.05 volumes of an organicextractant comprising 2-hydroxybenzophenoximes dissolved in kerosene andembodied in a floc of the synthetic ferromagnetic polymer prepared inExample 24 and designated resin D. A sin- 22 gle extracting stagereduced the copper in the effluent to 0.1 ppm. The organic extractantwas skimmed from the surface of the effluent by magnetic means, thecopper recovered by extraction and the organic extractant recycled.

We claim:

1. In the process of liquid/liquid extraction comprising extracting acompound from a solution of the compound in an aqueous liquid mediumwith a second or ganic liquid medium immiscible with the first liquidmedium, the improvement consisting of separating the two liquid phasesby firstly adding synthetic ferromagnetic polymeric particles beingcharacterised in that said ferromagnetic particles preferentially absorbor adsorb the second liquid medium; and secondly removing said particlestogether with the associated second liquid medium by magnetic means.

2. A process according to claim 1 wherein a complexing agent for thecompound to be extracted is added to one or both of said liquid mediaprior to extraction.

3. A process according to claim 1 wherein the second liquid medium is acomplexing agent for the compound to be extracted.

4. A process according to claim 1 wherein the second liquid medium isless than 10% w/w of the total composition.

5. A process according to claim 1 wherein the synthetic ferromagneticpolymer comprises a ferromagnetic particle incorporated wholly orpartially within polystyrene or copolymers of styrene and polyesters.

1. IN THE PROCESS OF LIQUID/LIQUID EXTRACTION COMPRISING EXTRACTING ACOMPOUND FROM A SOLUTION OF THE COMPOUND IN AN AQUEOUS LIQUID MEDIUMWITH A SECOND ORGANIC LIQUID MEDIUM IMMISCIBLE WITH THE FIRST LIQUIDMEDIUM, THE IMPROVEMMENT CONSISTING OF SEPARATING THE TWO LIQUID PHASESBY FIRSTLY ADDING SYNTHETIC FERROMAGNITIC POLYMERIC PARTICLES BEINGCHARACTERISED IN THAT SAID FERROMAGNETIC PARTILCES PERFERNTIALLY ABSORBOR ADSORB THE SECOND LIQUID MEDIUM; AND SECONDLY REMOVING
 2. A processaccording to claim 1 wherein a complexing agent for the compound to beextracted is added to one or both of said liquid media prior toextraction.
 3. A process according to claim 1 wherein the second liquidmedium is a complexing agent for the compound to be extracted.
 4. Aprocess according to claim 1 wherein the second liquid medium is lessthan 10% w/w of the total composition.
 5. A process according to claim 1wherein the synthetic ferromagnetic polymer comprises a ferromagneticparticle incorporated wholly or partially within polystyrene orcopolymers of styrene and polyesters.